Showing papers in "Marine Ecology in 1984"

Mass Mortality in the Gulf of Trieste: The Course of Community Destruction

Abstract: . Over a period of two weeks in September, 1983 a high biomass macroepifauna community characteristic of a greater part of the Gulf of Trieste suffered mass mortality. The affected area is estimated to cover several hundred km2. Within 2–3 days all sponges and the brittle star Ophiothrix quinquemaculata, which together make up over 60 % of the community biomass, were dead. Benthic fish, mostly gobiids, were already affected on the first day and littered the bottom in great numbers. Concurrently the complete spectrum of macroinfauna species including (in order of emergence) holothurians, burrowing shrimp, echinoids, polychaetes, sipunculids and bivalves appeared on the sediment surface. Within one week sea stars and all remaining ophiurids had died. At this time hermit crabs were found lying dead next to their shells. Several anemones survived into the last week, although many showed signs of severe stress and lay on the surface with exposed pedal discs. Oxygen deficiency is the apparent immediate cause of this phenomenon and several possible factors leading to anoxic conditions in the Gulf are discussed. This ecological catastrophy provides evidence that the affected community, considered to have achieved relative stability by developing a strategy effectively dampening the effect of physical oscillations, has a distinct tolerance limit to stress. The Gulf of Trieste, among the most productive areas in the Mediterranean Sea, must be considered as sensitive; September is a particularly critical month.

The ecology of marine hydroids and effects of environmental factors: a review

Abstract: . The history of the study of hydroid ecology is briefly outlined, pointing out the major methodological innovations which have contributed to the development of ecological research in the last thirty years. The influence of the major ecological factors on hydroid ecology and biology is synthesized, taking into account: substratum, water movement, light, salinity, sedimentation, exposure to air, temperature, food availability and pollution. Besides affecting the species composition of the hydroid community, these factors also influence the morphology and general biology of the individual species. The adaptations and reactions of hydroids to different intensities of the various environmental factors and to their combinations are reported.

Tropical Marine Fungi

Abstract: . Marine Ascomycetes, Basidiomycetes and Deuteromycetes were collected in tropical and subtropical regions (Australia, Belize, Fiji, Hawaii, Marshall Islands, Mexico, New Zealand, Palau, Thailand), and the known range of distribution for these fungi was extended. Exclusively tropical are 27 taxa, 9 are probably restricted to the tropics also, and 11 are cosmopolitan. Distribution maps are given for 5 taxa. New species (4), varieties (3), and combinations (2) of Ascomycetes are proposed, and keys to the taxa of Halosarpheia and Lulworthia are presented. Most of the species are decomposers of mangrove parts or of detritus in sandy beaches. Nine new host plants were found. Marine Ascomycetes were discovered for the first time living in shells of foraminifera.

Resource Management of Precious Corals

Abstract: . Precious corals as a group consist of a variety of species which belong to several classes of Anthozoan corals. In general, all are long lived, slow growing and are characterized by slow rates of annual recruitment and adult mortality. In favorable environments, where large beds of commercial quantity exist, their life history parameters often approximate steady state. In such instances, fishery management models in which the assumption of steady state is explicit, can be applied to their management. In this paper, the history and ecology of precious corals are reviewed in light of modern attempts of resource management using fishery models. In Hawaii, the BEVERTON and HOLT model has been adapted for the management of black, pink and gold coral species. The application of this model as it applies to precious corals is described and an example is given illustrating that it can also be used for shallow water reef building corals which form discrete colonies.

A Study in Ultra‐Ecology: Microorganisms on the Seagrass Posidonia oceanica (L.) DELILE

Abstract: . Microbial colonization on the leaves of a shoot of the mediterranean seagrass Posidonia oceanica (L.) DELILE was studied using Scanning Electron Microscopy. Methods of field ecology such as transect, random plot and stratified sampling survey were applied to the microbial niveau to gain both qualitative and quantitative information on the microbial assemblage. While macro-epiphytic growth was significantly greater on the outer leaf sides, microbial colonization density was significantly higher on the inner leaf sides, both on leaf surface and epiphyte surface. Diatoms colonized the surface of incrusting algae and epiphytic animals in significantly lower numbers than the Posidonia leaf surface and were absent on erect epiphytic algae. Bacterial densities on epiphyte surfaces even exceeded values of the corresponding leaf surfaces on algal thalli near the leaf tips and on old leaves. Diatoms reach highest mean density on mature leaves and close to the leaf tips, while bacteria reach their greatest density on the oldest leaf and closer to the leaf base. Diatom density in general increases with exposure time of plant surface, while greatest bacterial density was observed at 7–10 weeks exposure. Basal leaf parts on younger leaves were dominated by rod-shaped bacteria, while distal leaf parts and old leaves were dominated by small coccoid bacteria. Surfaces of epiphytic algae were always distinctly dominated by small coccoid bacteria, and edges of thalli attracted high microbial densities. Microbial biomass (calculated from cell volumes using standard conversion factors) amounts to 2.3 g dry weight m-2 in the Posidonia stand where the shoot was sampled. The observed patterns of epiphytic colonization are interpreted as the result of a complex, dynamically changing system of interactions both within the epiphytic community and between the epiphytic community, the host plant, and it's environment. A model of the organization of the epiphytic community on Posidonia leaves is presented. “Ultra-ecology” is a term introduced to denote a type of SEM research in the micro-environment which is analogous to in situ investigation in “macroscopic” ecological work.

Brittlestar Color-Change and Phototaxis (Echinodermata: Ophiuroidea: Ophiocomidae).

Abstract: . In the first decisive study of color-change in brittlestars, four Caribbean species, Ophiocoma echinata, 0. paucigranulata, O. pumila, and O. wendti are reported to change color from day to night. Color-change is most striking in O. wendti, which is dark brown during the day, and is banded gray and black from dusk to dawn. The transformation occurs over a 3 to 4 hour period and is effected by chromatorphores which appear to respond to illumination, independently of the central nervous system. Color-change may also be mediated by an endogenous rhythm. Ophiocoma wendti is more responsive to light than the other 3 species tested. It reacts to lower levels of illumination at night than during the day, exhibiting negative phototaxis in moonlight as well as in sunlight. I suggest that color-change may expose (or shield) photosensitive tissues that control the brittlestar's detection of shaded fissures in the reef. Thereby, chromatophore activity may be connected with the brittlestar's chief defense from predators, the ability to detect shadow and escape into darkened crevices. Although experiments to date with predacious fish are equivocal. the color patterns of Ophiocoma species mav provide protective camouflage.

The Association of Ophiothrix lineata and Callyspongia vaginalis: A Brittlestar‐Sponge Cleaning Symbiosis?

Abstract: . The relationship between a sponge, Callyspongia vaginalis, and an associated brittlestar, Ophiothrix lineata, was examined for mutualistic symbiotic interaction. Cinematography, feeding experiments, and analyses of stomach contents reveal that O. lineata (unlike other Ophiothrix species) is a non-selective deposit feeder. Its diet consists of detrital particles adhering to the sponge, which are too large to be utilized by the sponge as food. Thus, the brittlestar cleans the inhalent surface of the sponge as it feeds. Since siltation interferes with sponge pumping-activity, it is suggested that the cleaning behavior of O. lineata may enhance the filtration capability of C. vaginalis. In situ elapsed-time films show that brittlestars expose their arms when they feed, suggesting that they feed only at night because of a need to avoid diurnal predators. Manipulative experiments show that residence in C. vaginalis protects O. lineata from predatory fish. A comparison of the incidence of arm regeneration for brittlestars residing on C. vaginalis, and on a toxic sponge, Neofibularia nolitangere, indicates that factors other than sponge toxicity are involved in protecting sponge-dwelling brittlestars.

Zooplankton Feeding Ecology: Contents of Fecal Pellets of the Copepods Acartia tonsa and Labidocera aestiva from Continental Shelf Waters Near the Mouth of the Mississippi River

Abstract: . Feeding habits of adult female Acartia tonsa and Labidocera aestiva and L. aestiva CV copepodites were examined by comparing fecal pellet contents and available phytoplankton. Samples were collected from eight stations in the northern Gulf of Mexico near the mouth of the Mississippi River. Fecal pellets of both copepods contained remains of a wide variety of chain-forming and solitary phytoplankters of various sizes, as well as remains of other crustaceans. Contents of fecal pellets generally mirrored the composition and relative abundance of fluctuating assemblages of available natural phytoplankton. Both species fed upon a wide size range of cells, from solitary centric diatoms of 2–8 um diameter up to large solitary centrics of 33–53 urn diameter. Both copepods also ingested the elongate solitary pennate diatom Thalassiothrix sp. (264–330 urn long) and chain-forming diatoms such as Skeletonema costatum. Remains of large or chain-forming diatoms and crustaceans were more dominant in fecal pellets of L. aestiva. This suggests that L. aestiva is primarily a raptorial feeder, grasping larger particles while A. tonsa is a more typical suspension feeder. Both copepods are opportunistic omnivores, however, and there is considerable overlap in their diets.

Temporal and Morphological Variations of Growth in a Natural Stand of Posidonia oceanica (L.) Delile

Abstract: . Growth of Posidonia oceanica (L.) DELILE was studied in a natural stand in 4 m depth at Ischia (Gulf of Naples). Renewal and growth of leaves was continuous throughout the year but showed strong seasonal modulation. The major factor for individual leaf growth as well as for the seasonal aspects of the entire foliage is seasonal modulation of leaf appearance rather than of leaf growth. Leaf area index varied between 2 nm2 m-2 in autumn and 6 m2 m-2 in late summer. Annual production is estimated to be 613 g dw m-2 for leaf blades, 54 g dw m-2 for leaf sheaths, and 27 g dw m-2 for rhizomes. Rhizome production is highly different between the primary and the secondary growth axis (274 versus 30 mg dw -shoot-1 y-1 respectively) in plagiotrope growth. Both foliage and rhizome growth are positively correlated with leaf width.

A Quantitative Study of the Stony Coral Fishery in Cebu, Philippines

Abstract: . The Philippines is generally accepted to be the center of the international trade of stony corals for ornamental use. Despite existing legal bans on the collection and export of stony corals in the Philippines, the coral trade continues to date, particularly in Cebu. This paper reports on the specific market demand for stony corals in Cebu and the effects of commercial collection based on the results of a quantitative study of two shallow coral reef areas subjected to large differences in collection effort. Comparison of the measured coral community parameters suggests selective population changes and reduced abundance of exploited coral populations as a result of commercial collection. Estimates of the natural mortality, fishing mortality and yield are presented for the two sampled populations of Pocillopora verrucosa, utilizing the method of GRIGG (1976). Based on the study results and a review of reported coral growth rates and coral colony size at reproductive maturity, the potential for resource management of stony corals on a sustainable yield basis is - discussed.

The Role of Isopod Crustaceans in the Reef Crest Community at Carrie Bow Cay, Belize

Abstract: . The species composition and numbers of specimens of isopod crustaceans from the rubble of a Belizean reef crest were obtained. Four sets of 30 samples were taken from three rubble zones (rubble with algal turf, rubble between Thalassia plants, and pure rubble), in four different collecting periods. Twenty-four species of isopods were identified, sexed and counted. By means of a Likelihood Ratio Chi-square Contingency Table Analysis the presence of 13 species was shown to be positively correlated with habitat, 15 species with season, and nine species with habitat and season combined. From the spread of total numbers and of ovigerous females it is proposed that the isopods may be grouped into three patterns: a) those present and breeding in the reef crest rubble throughout the year, i. e. stress-tolerant species; b) those showing a breeding peak in summer and a population decrease in winter-spring, i. e. opportunist species; and c) those showing a breeding peak in the fall, and a second peak in spring, and a decrease or complete avoidance of the habitat, especially by ovigerous females, in the summer. The diversity of the Belizean reef crest isopod fauna is compared with the published report of the isopod fauna of a coral reef in Madagascar. Several similarities in composition are noted. The multiplicity of microhabitats is invoked as a possible explanation for the relatively high diversity of anthuridean isopods in coral reefs.

Dietary Shifts in the Queen Triggerfish, Balistes vetula, in the Absence of its Primary Food Item, Diadema antillarum

Abstract: . The long-spined sea urchin Diadema antillarum has been reported to be the major food item of the queen triggerfish, Balistes vetula in the Caribbean. This sea urchin has undergone a massive mortality on reefs throughout the Caribbean during 1983. The dietary habits of twenty-three queen triggerfish from patch reef habitats in Belize were examined. It was found that crabs and chitons now form the major dietary items when D. antillarum is not available. It is suggested that this predator, which was previously specialized on a single food item, is able to shift resource utilization in the absence of its primary food source, and that the queen triggerfish can capture diverse prey from a wide variety of habitats.

Subtidal benthic macroinfauna in an estuary of South Chile: distribution pattern in relation to sediment types

Abstract: . A quantitative survey (18 stations) of the subtidal soft bottom macroinfauna in an estuary of the south Chilean coast was conducted during January, 1980. The map of sedimentological facies elaborated for the Queule River Estuary shows sandy bottoms in the outlet and upper part of the area studied, while the middle part is occupied by muddy sand. The ordination of stations by Principal Component Analysis is fundamentally defined by mud and gravel percentage and is, in general, concordant with the distribution of sediments in the facies map. A total of 17,405 animals was collected (16 taxa), Polychaeta being the dominant group in density (77.47%) and biomass (73.4%). The maximum number of species was obtained outside the mouth of the estuary, while maximum densities and biomass were obtained in the middle of the estuary. The Factor Analysis performed with the abundances data of the most abundant species rendered the ordination of two groups of stations (concordant with a Cluster Analysis) in the Q-mode and two groups of species in the R-mode. One group of stations is restricted to sandy habitats of the outlet area and is dominated by suspension feeders. The other, in the middle and upper part of the estuary (muddy sand or sandy bottoms with a higher percentage of organic matter), is dominated by deposit feeders. Between these two groups, significant differences in sedimentological variables (sand, mud, and organic matter percentage) were detected. Each of the two delineated groups of species corresponds to the groups of stations, showing that most of the taxa can be combined in faunal assemblages with preference for different types of substrate.

The Ectoparasitic Gastropod Boonea (= Odostomia) impressa: Population Ecology and the Influence of Parasitism on Oyster Growth Rates

Abstract: . Boonea (= Odostomia) impressa is a common ectoparasite of oysters. In the laboratory, small oysters (Crassostrea virginica) parasitized by natural densities of B. impressa produced 75 % less new shell than unparasitized oysters. Shell deposition rates of previously parasitized oysters increased significantly after all B. impressa were removed. Thus, the decrease in growth rate, although significant, apparently was not permanent. B. impressa preferentially parasitized small, living oysters (≤2.5cm) in the field, even though a higher percentage of large, living oysters (>2.5cm) was available. The snails maintained an aggregated distribution on the oyster reef. The number of B. impressa per oyster clump was positively correlated with the number of living oysters per clump, however some clumps with few or no living oysters had many B. impressa. Thus, food availability only partially explained the pattern of distribution. B. impressa was very mobile. About 50 % of the population moved in one week. Reproduction occurred throughout the year with a peak period in May. Recruitment was greatest in July, however new recruits were observed throughout the year. The reduction in growth rate of parasitized oysters, the snaiľs propensity towards parasitizing small oysters and the snail's tendency to be contagiously distributed suggests that B. impressa potentially exerts a significant influence on the population structure and health of oyster populations.

The Benthic Phase of the Life Cycle of Penaeus semisulcatus De Haan (Crustacea Decapoda) along the Southeastern Coast of the Mediterranean

Abstract: . Recruitment, migration, growth and longevity of populations of Penaeus semisulcatus along the southeastern coast of the Mediterranean were investigated. The general pattern of the life cycle of P. semisulcatus and the parameters affecting it were identified. Relative population density, measured by catch per unit effort, as well as relative age estimated by age group body length were used to study the pattern of the benthic phase of the life cycle.

Cocoon deposition on three crab species and fish parasitism by the leech Notostomum cyclostoma from deep fjords in northern British Columbia.

Abstract: Cocoons of the sanguivorous piscicolid leech Notostomum cyclostoma (Johansson) were found on 3 crab species, Lithodes aequispina, Paralithodes camtschatica and Chionoecetes bairdifrom deep fjords in the Portland Inlet system, northern British Columbia, Canada. This leech-crab associa- tion is convenient for cocoon deposition and dispersal. The leech does not appear to harm its crab hosts. Gut contents of N. cyclostoma collected off the crabs were fish-blood meals in various stages of digestion. The haemoflagellate Cryptobia sp. was observed in gut and proboscis area of 90 % of the leeches. One leech harbored another haemoflagellate, Trypanosoma sp., in its gut. Cryptobia sp. and Trypanosoma sp. were observed in the blood of 29 % of yellowfin soles Limanda aspera from one fjord. No haemoflagellates were observed in 7 other fish species caught coincidentally with the crabs. L. aequispina was the most cocoon - infested crab species. In Observatory Inlet, where L. aequispina was least common, more cocoons per crab were recorded than from the other fjords, Alice and Hastings Arms. Crabs which had not moulted for some time carried more cocoons than those with newer shells. This was less marked among C. bairdi subject to the exoskeleton disease of Black Mat Syndrome on older shells. The most used cocoon deposition site on crabs was the carapace, followed by the merus segments of the posterior limbs.

Coarse‐Scale Horizontal Distribution of Phytoplankton in a Semi‐Enclosed Coastal Area

Abstract: . The horizontal distribution of phytoplankton in relation to changes in the physico-chemical conditions of a eutrophic semi-enclosed embayment is described. Phytoplanktonic populations derived from a station interval of 6 miles (coarse scale variations) were compared by quantitative (standing stock) and qualitative (species composition, diversity, Diatom/Flagellate ratio) criteria. The results showed that quantitative and qualitative parameters differed in their sensitivity and were affected differently by environmental perturbations. Along a horizontal transect with defined variations in nutrient concentrations, changes in standing stock levels were not significant, but differences in species composition existed and caused coefficients of variation between stations for species diversity up to 50% and of the Diatom/Flagellate ratio up to 120%. Furthermore, distributional differences among certain flagellate species (Prorocentrum micans, Prorocentrum balticum) and diatom species (Nitzschia closterium, Chaetoceros curvisetus) were recorded which showed that the flagellate species were distributed more uniformly than the diatoms along a transect with progressive decrease in nutrient concentrations.

The Role of Higher Trophic Levels in a Sublittoral Benthic Community

Abstract: . The ingestion of carnivores and omnivores was determined during the investigation of higher trophic levels in a North Adriatic benthic community. The ingestion rate was calculated from respiration data using a respiration-production equation and an assumed assimilation efficiency. In the case of the starfish Astropecten aranciacus the ingestion rate obtained by this indirect method was in good agreement with the ingestion rate calculated directly from gut contents, taking the retaining period of food items in the gut into consideration. These results are compared to previously published ingestion rates. The influence of A aranciacus on the community is briefly discussed.

Variability of Coulter Counter Data and their Relationship with Other Oceano‐graphical Parameters

Abstract: . Coulter counter data (from the upper 100 m of water) gathered during a cruise in October, 1976 in the Spanish waters of the Western Mediterranean are analysed in this paper. The ANOVA shows that the main sources of variability are the geographical situation and the depth level, while the sampling method especially affects the results for the larger particles. Repeating the counting in the same sample also introduces some changes which have less importance in the overall sense. Correlations of the particle counts with chlorophyll a, total POC and PON, POC and PON above 200u.m, estimated POC based on the particle size spectra, and SECCHI disc visibility were calculated and are discussed in order to assess the kind of information given by seston counts obtained from two different sampling methods and expressed both in absolute values (ppm by volume) and as a percentage of volume for the different channels. Some striking results arise which suggest that the use of a Coulter counter together with some kind of sample treatment might give an insight into the qualitative and quantitative characterization of the pelagic ecosystem.

Influence of Certain Organic Substances on Growth and Colony Formation of Asterionella glacialis Castracane (Bacillariophyceae)

Abstract: . Organic substances are suspected to influence the unpredictable, episodic blooms which characterize the planktonic pennate diatom Asterionella glacialis in certain coastal waters. Experiments to test its general responsiveness to organic enrichments in terms of growth rate and colony formation were carried out. An axenic clone was grown at 10° C, 0.039 l min-1,12:12 LD cycle in Guillard's f/2 medium enriched with eight different organic substances. Growth rates in organically-enriched media during exponential phase usually exceeded those in f/2 medium alone. Cell yields after 12 days in media enriched with glycyl-glycin and trypticase + yeast extract were significantly greater than in the other treatments. Longer chain lengths accompanied organic enrichment, notably with trypticase + yeast extract and 100ppm soil extract. These results suggest that Asterionella glacialis is positively responsive to elevated levels of certain organic substances. A potential effect of organic substance - trace metal - silica interactions on colony-size is suggested.

Der Einfluß einiger aÜßerer Faktoren auf die geschiechtliche Entwicklung und die Segmentbildung bei Anaitides mucosa (Annelida, Polychaeta, Phyllodocidae)

Abstract: . The influence of some exogenous factors (temperature, day-length, starving, amputation of caudal segments) on oocyte development and on somatic growth in the polychaete Anaitides mucosa has been investigated. Animals from Wimereux (France) were maintained in the laboratory from September to April. Like in other polychaetes with a breeding season in early spring oocytes grow in two waves. The second one only occurs after spawning of the first and shows an accelerated growth. Low temperatures (5 oC) (i. e. winter conditions) are essential for a qualitative normal development of the first wave, whilst higher temperatures (15 oC) totally suppress maturation of oocytes and reproduction. The influence of day-length, however, is probably without importance. Starving and amputation of caudal segments to do not produce significant changes in the growth rate of oocytes, either. In contrast, the somatic growth is most extensive at high temperatures (15 oC) and long-day photoperiods (LD 16/8). Zusammenfassung Eine normal verlaufende Entwicklung der Oocyten von Anaitides mucosa findet nur wahrend einer langeren Periode mit niedrigen Temperaturen (5oC) statt. Hungerbedingungen und Regenerationsprozesse, ausgelost durch die Amputation caudaler Segmente, beeinflussen die Entwicklung der Oocyten bei niedrigen Temperaturen nicht. Die Oocytenentwicklung ist nicht abhangig von der Photoperiode. Das somatische Wachstum ist dagegen an hohere Temperaturen (15 oC) und in geringerem Umfange an Langtag-Bedingungen (LD 16/8) gebunden.